1. Field of the Invention
The present invention relates in general to a door locking system for vehicles and particularly to an automotive door locking system of the type having an antitheft deadlocking or safety mechanism.
2. Description of the Prior Art
A known door locking system is provided with an antitheft deadlocking or safety mechanism adapted to hold a locking lever, which is movable between a locking position and an unlocking position for locking and unlocking the locking mechanism, in the locking position and prevent movement of the locking lever out of the locking position when the locking mechanism has been locked by a lock cylinder which is manually operated from the outside of the door with a key. Insofar as the safety mechanism blocks movement of the locking lever out of the locking position, the locking mechanism cannot be unlocked by a locking button which is manually operated from the inside of the door. By this, it is intended to attain an improved antitheft effect.
FIGS. 4 and 5 show an example of a prior art door locking system of the above described kind.
In the figures, 1 is a locking mechanism installed on a door "D". 2 is a lock cylinder disposed adjacent an outside door handle 3 and adapted to be operated from the outside of the door "D" with a key. 4 is a locking button installed on a waist portion of the door "D" in such a way as to project upward therefrom and adapted to be operated from the inside of the door "D". 5 is an inside door handle. 6 is a locking lever fixedly attached to a locking shaft 7 of the locking mechanism 1 and movable between a locking position and an unlocking position for locking and unlocking the locking mechanism 1. The locking lever 6 is connected via pull rods 8 and 9 to the lock cylinder 2 and the locking button 4 so that the operation of the locking mechanism 1 can be controlled via the pull rods 8 and 9 by the lock cylinder 2 and the locking button 4. 10 is an antitheft deadlocking or safety mechanism which is provided with an electric actuator 11. The actuator 11 has a reciprocative rod 12 which is movable between an engaging position and a disengaging position where the rod 12 engages in and disengages from a recessed portion 13 of the locking lever 6 under drive of a drive means which is electrically actuated. By the operation of the safety mechanism 10, the locking lever 6 is selectively locked and unlocked.
The operation of the safety mechanism 10 is controlled on the basis of a signal from a detector (not shown) provided to the lock cylinder 2 to detect whether the lock cylinder 2 is operated toward a locking position or an unlocking position with a proper key. When the locking mechanism 1 has been locked by the operation of the lock cylinder 2, the safety mechanism 10 is electrically actuated or operated to lock the locking lever 6 in the locking position. When the locking mechanism 1 is unlocked by the operation of the lock cylinder 2, the safety mechanism 10 unlocks the locking lever 6.
14 is a pull rod connecting between the outside handle 3 and the locking mechanism 1, and 15 is a pull rod connecting between the inside handle 5 and the locking mechanism 1.
A similar door locking system of the above described kind is disclosed in "New Car Service Manual for Passat 319A", published on May, 1990 by Nissan Motor Co., Ltd. and GB 2,034,802.
A problem of the door locking system of the above described kind is that when a storage battery has been discharged or has been removed so that there is no supply of current to the safety mechanism, the safety mechanism becomes inoperative, so when the storage battery is discharged under a locking condition of the safety mechanism, i.e., under a condition in which the locking lever is locked by the operation of the safety mechanism, it becomes impossible to unlock the locking mechanism even by the lock cylinder which is operated with a key.